Roadwork is typically carried out by working machines that carry one or more working components and travel along a roadway. One such working machine is a milling machine, a wheeled or track-driven vehicle that is provided with a rotating working drum that includes a plurality of cutting teeth. The drum is mounted in a housing on the frame of the machine and adapted to be lowered into contact with the road surface and rotated about a horizontal axis so as to cut into the surface to a desired depth as the machine is advanced along the roadway. Generally, the milling machine also includes a conveyor system that is designed to carry the milled material which has been cut from the roadway by the rotating drum to a location in front of, to the rear of, or beside the machine for deposit into a truck for removal from the milling site. One or more spray assemblies are typically mounted over the conveyors and inside the drum housing so that water may be sprayed to control the dust and heat that is generated in the milling process. Generally, it is necessary to provide a water spray at relatively high flow rates in order to control the heat and dust generated during a milling operation. If the machine is used for cold in-place recycling, a second spray assembly may be provided to spray an asphalt emulsion or liquid asphalt cement onto the milled material. Steerable track or wheel drive assemblies are provided to drive the machine and to steer it along a desired milling path. Power for driving the machine and for operating its systems is typically provided by a diesel engine.
Another type of working machine is a road stabilizer/reclaimer machine. This machine is similar to a milling machine in that it comprises a wheeled or track-driven vehicle that includes a milling assembly comprising a milling drum with a plurality of cutter teeth mounted thereon which is contained within a milling enclosure or chamber. However, the milling drum of a road stabilizer/reclaimer machine is generally employed to mill or pulverize an existing road bed or roadway to a greater depth than does a milling machine prior to repaving (usually called reclaiming) or prior to initial paving (usually called stabilizing), and it leaves the pulverized material in place. A water spray assembly, similar to that provided in a milling machine, is provided to control the dust and heat that is generated in the milling or pulverizing process. If the machine is used for cold in-place recycling, a second spray assembly may be provided to spray an asphalt emulsion or liquid asphalt cement onto the pulverized material.
When a milling or stabilizing operation has been completed, paving of the roadway with asphalt paving material is generally carried out by another working machine. An asphalt paving machine is supplied with asphalt paving material by a number of supply trucks and/or a material transfer vehicle. The paving machine is self-propelled and driven by a wheeled or track drive system. In a common type of paving machine, an asphalt receiving hopper is located at the front end of the machine to receive asphalt paving material from a truck or material transfer vehicle, and a hopper conveyor located below the asphalt receiving hopper transfers the asphalt paving material from the hopper to an asphalt distributing assembly comprising a transverse distributing auger that is mounted near the rear of the machine. The asphalt paving material is deposited onto and across the roadway or other surface to be paved by the distributing auger, and a floating screed located at the rear end of the machine behind the distributing auger compacts the asphalt paving material to form an asphalt mat.
It is frequently desirable to apply an asphalt emulsion, liquid asphalt cement or a similar substance (commonly referred to as “tack” or “tack material”) onto the surface of the roadway prior to distributing and compacting the asphalt paving material into a mat to assist in binding the asphalt paving material to the underlying surface. Tack is typically applied just prior to a paving operation by being sprayed onto the surface to be paved from a spray bar or spray assembly that extends transversely across the surface. Some asphalt paving machines include a tack spray assembly that is adapted to deposit tack material onto the surface of the roadway ahead of the distributing auger. Sometimes the tack material is applied by another working machine, a tack distributor truck that travels ahead of the asphalt paving machine.
The various spray assemblies that are found on milling machines, stabilizer/reclaimer machines, asphalt paving machines and tack distributor trucks typically include a plurality of spray nozzles, each of which is actuated by a poppet valve. Direct fluid actuation of the valves associated with the spray assemblies has not been considered to be practical, because the flow rates for water sprays through the valve assemblies in working machines are too high to reliably open and close the valves, and the hot asphalt cements and emulsions used in asphalt paving materials or tack sprays are so viscous that they will “freeze” in the valve assemblies. Consequently, these spray assemblies generally employ smaller pilot-controlled valves that use an intermediate power transmission fluid such as air or hydraulic fluid to control the opening and closing of the spray valves. Such a valve assembly is generally quite reliable, but it requires a separate fluid circuit for the pilot fluid, and multiple fluid lines between the small control valves and the poppet valve assemblies. It would be desirable if a spray assembly for a working machine could be provided that could employ a simpler but reliable control system.